As disclosed in U.S. Pat. No. 4,594,453 (Ranken et al.), it is known that various (hydrocarbylthio) aromatic amines are useful as intermediates in the preparation of biologically active materials, polyurethanes, etc., and they can be prepared by reacting an aromatic amine with a hydrocarbyl disulfide in the presence of a Lewis acid catalyst. The preferred catalysts of Ranken et al. are metal halides, such as aluminum chloride, boron trifluoride, boron trichloride, ferric chloride and zinc chloride.
U.S. Pat. No. 4,670,597 (Ranken et al.) discloses the preparation of (hydrocarbylthio) aromatic amines by the hydrocarbylthiolation of aromatic monoamines with a hydrocarbyl disulfide in the presence of Lewis acid catalysts selected from hydrogen iodide, ammonium iodide, and copper iodide.
U.S. Pat. No. 4,751,330 (Davis) discloses the preparation of (hydrocarbylthio) aromatic amines by the hydrocarbylthiolation of aromatic amines in the presence of metal or metal halide catalysts, with particularly good results noted with the use of copper, zinc, or ferric, ferrous, or aluminum chloride.
U.S. Pat. No. 4,825,002 (Davis) discloses the removal of a Lewis acid contaminant from a (hydrocarbylthio)aromatic amine by mixing a solid alkali metal hydroxide with a solution of the Lewis acid in the (hydrocarbylthio)aromatic amine, preferably at about 110.degree.-120.degree. C., and then filtering the solids from the mixture.